1. Field of the Invention
The invention relates to a metallic vacuum housing for an X-ray tube of the type having an anode and a cathode arranged inside the metallic vacuum housing.
2. Description of the Prior Art
An X-ray tube essentially has a cathode and an anode that are arranged in a vacuum-tight evacuated housing which substantially may be made out of a metallic material. The cathode emits, during operation of the X-ray tube, an electron beam that strikes the anode at an impact zone that usually is formed by a layer of a tungsten-rhenium alloy. When striking the anode, several electrons of the electron beam are decelerated and produce X-ray photons. Some of the electrons of the electronic beam, however, are scattered rather than decelerated. Scattered electrons may strike the surface of the vacuum housing. An X-ray tube with a metallic vacuum housing is, for instance, described in U.S. Pat. No. 5,909,479.
Scattered electrons striking the metallic vacuum housing may stress the housing thermally. The thermal stress can produce cracks in the metallic vacuum housing eventually causing a leakage of the vacuum housing. Failure of the X-ray tube because of a leakage of its metallic housing due to scattered electrons may be even more likely if scattered electrons preferentially strike a certain area of the vacuum housing.